Identification and analysis of eight peptide transporter homologs in rice

Peptide transporters (PTRs) have diverse substrates and underlie many biological processes in plants. To better understand their function and regulation, we have analyzed the transport capabilities of eight rice PTRs (OsPTRs) in a yeast ptr2 mutant strain and their expression patterns in plants. A yeast ptr2 complementation assay demonstrated that only OsPTR6 transports Gly–His and Gly–His–Gly, and OsPTR6 shows substrate selectivity for di-/tripeptides; however, the other seven proteins could not transport the five tested di-/tripeptides. The expression patterns for the eight OsPTRs were distinct in tissues under normal growth conditions. In germinating seeds, seven of the eight OsPTRs were expressed at various levels, but OsPTR5 was not expressed. In grain-filling seeds, expression of OsPTR4, OsPTR7 and OsPTR8 increased from early to late stages of seed development and that of OsPTR2, OsPTR3 and OsPTR6 decreased. Expression of OsPTR1, OsPTR2, OsPTR5, OsPTR7 and OsPTR8 were upregulated by drought and salt, and OsPTR4 was downregulated. However, only OsPTR1 displayed a slight upregulation by cold. This study showed that rice OsPTRs have distinctive transport functions for substrates and differing expression patterns during both development and response to stress.

Research highlights▶ OsPTR6 can transport di-/tripeptides with substrate selectivity. ▶ The eight OsPTRs showed distinct expression pattern. ▶ The eight OsPTRs had different responses to the salt, drought and cold treatments.